Screw

ABSTRACT

A screw includes a shank and at least one end cutting groove. The shank includes a lower section disposed near an insertion end thereof and an upper section disposed near a head end thereof. The lower section has triangular transverse cross sections, and the upper section has circular transverse cross sections. A first thread is disposed on the lower section of the shank, and a second thread is disposed on the upper section of the shank. A non-threaded section is disposed between the lower section and the upper section of the shank. An outer diameter of the non-threaded section is larger than an outer diameter of the upper section. The end cutting groove is formed in the lower section of the shank, and an included angle between 3 and 9 degrees is formed between an extending direction of the end cutting groove and a longitudinal axis of the shank.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation-in-part application of U.S. patent applicationSer. No. 13/866,091 filed Apr. 19, 2013, now U.S. Pat. No. 8,926,249.

BACKGROUND OF THE INVENTION

The present invention relates to a screw and, more particularly, to ascrew adapted to be used in wood, construction materials, and similarmaterials.

A large amount of wood or compound wooden materials mixed and compressedfrom plastic resin and wood chips are used to produce wooden work-piecesfor furniture, decoration and construction, and screws are often used inconnection between wooden work-pieces.

A conventional screw 10 for using with wood is shown in FIG. 1. Thescrew 10 includes a round shank 12 and a thread 14 disposed on the shank12. The shank 12 includes an insertion end 16 and a head end 17. Theinsertion end 16 has an end cutting groove 18. When the screw 10 isscrewed into a to-be-connected work-piece with the insertion end 16, theend cutting groove 18 is used for cutting the work-piece, so that thethread 14 can be screwed into the work-piece smoothly. However, becausethe cross section of the shank 12 of the screw 10 in FIG. 1 is round, arelatively larger friction force is produced from the full contactbetween the thread 14 and the work-piece when the thread 14 is screwedinto the work-piece, which will require more effort and time inoperation. Furthermore, the end cutting groove 18 of the screw 10extends axially along the shank 12, making it difficult for wood chipsproduced from cutting to be expelled smoothly. Therefore, the screw 10is obstructed by the waste chips during the process of screwing into thework-piece, which will require more effort in operation, and thework-piece will easily crack because of compression. Additionally, whenthe screw 10 is used for screwing into compound sheets mixed andcompressed from plastic resin and wood chips, the waste chips can not beeffectively cut off, because the end cutting groove 18 of the screw 10extends axially along the shank 12, and because obstructions will beproduced when the screw 10 is screwed into the compound sheets.

Conventional screws 10 a and 10 b used for screwing into compound sheetsmixed and compressed from plastic resin and wood chips are shown inFIGS. 1A and 1B respectively. Each of the screws 10 a and 10 b includesa shank 12 and a thread 14 disposed on a lower section of the shank 12.The shank 12 includes an insertion end 16 and a head end 17.Furthermore, the thread 14 of the screw 10 a in FIG. 1A near theinsertion end 16 has a smaller thread height favorable for screwing intothe compound sheet surfaces. V-shaped grooves 19 are disposed in thethread 14 favorable for the expelling of waste chips produced from thescrewing of the screw 10 a. However, the speed of screwing of the screw10 a into the compound sheets is relatively slow. Specifically, thethread convolutions with smaller thread height are designed for allowingthe screw 10 a to screw into the compound sheets slowly, so that thereis more time for the waste chips to be expelled. Additionally, theV-shaped grooves 19 of the screw 10 a can not effectively cut off thewaste chips. As for the screw 10 b in FIG. 1B, even though the screw 10b can be screwed into the compound sheets with faster speed, the thread14 of the screw 10 b can not effectively cut off the waste chips. As aresult, the screw 10 b will be obstructed by the waste chips when it isscrewed into the work-piece, and the compound sheets will, therefore,crack easily.

BRIEF SUMMARY OF THE INVENTION

It is an objective of the present invention to provide a screw suitablefor using in wood and construction materials. The screw can effectivelyreduce the frictional resistance when the screw is screwed into awork-piece, so that the screw can be screwed into the work-piecespeedily, and so that an upper section of a shank of the screw can belocked into the work-piece smoothly.

To achieve this and other objectives, a screw of the present inventionincludes a shank and at least one end cutting groove. The shank includesan insertion end and a head end spaced from the insertion end along alongitudinal axis. The shank further includes a lower section disposednear the insertion end and an upper section disposed near the head end.The lower section has a rough triangular transverse cross section, andthe upper section has a circular transverse cross section. A firstthread is spirally disposed on an outer circumference of the lowersection of the shank and includes a plurality of asymmetrical threadconvolutions. A second thread is spirally disposed on an outercircumference of the upper section of the shank. A non-threaded sectionis disposed between the lower section and the upper section of theshank, and an outer diameter of the non-threaded section is larger thanan outer diameter of the upper section. The end cutting groove isdisposed in the lower section of the shank and extends from theinsertion end toward the head end upwardly and slantingly. An includedangle is formed between an extending direction of the end cutting grooveand the longitudinal axis and is between 3 and 9 degrees.

In an embodiment, the screw includes two end cutting grooves oppositealong a circumference direction of the shank. The upward extendingdirection of each of the end cutting grooves is the same as the upwardspiral direction of the first thread. An upward spiral direction of thesecond thread is opposite to that of the first thread.

Preferably, each of the asymmetrical thread convolutions of the firstthread has a first cutting surface and a second cutting surface. Anincluded angle between the first cutting surface and a horizontal axisperpendicular to longitudinal axis is between 15 and 25 degrees, and anincluded angle between the second cutting surface and the horizontalaxis is between 5 and 15 degrees. A plurality of circularly protrudingteeth is formed and spaced apart around an outer surface of thenon-threaded section.

The present invention will become clearer in light of the followingdetailed description of illustrative embodiments of this inventiondescribed in connection with the drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a conventional screw.

FIG. 1A is a schematic view of a conventional screw for using incompound sheets.

FIG. 1B is a schematic view of another conventional screw for using incompound sheets.

FIG. 2 is a perspective view of a screw according to a first embodimentof the present invention.

FIG. 3 is an elevational view of the screw of FIG. 2.

FIG. 4 is a partial, enlarged view of the screw of FIG. 3 with anotherend cutting groove opposite to the end cutting groove in FIG. 3 beingshown.

FIG. 5 is sectional view taken along line 5-5 of FIG. 3.

FIG. 6 is sectional view taken along line 6-6 of FIG. 3.

FIG. 7 is sectional view taken along line 7-7 of FIG. 3.

FIG. 8 is an enlarged view of a circled portion of FIG. 4.

FIG. 9 is a perspective view of a screw according to a second embodimentof the present invention.

FIG. 10 is a view illustrating use of the screw of FIG. 2 coupled withtwo work-pieces.

FIG. 11 is an elevational view of a screw according to a thirdembodiment of the present invention.

FIG. 12 is a view illustrating use of the screw of FIG. 11 coupled withtwo work-pieces.

FIG. 13 is an elevational view of a screw according to a fourthembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A screw according to a first embodiment of the present invention isshown in FIGS. 2 through 8 of the drawings and generally designated 20.The screw 20 includes a shank 22 having an insertion end 24 and a headend 26 spaced from the insertion end 24 along a longitudinal axis. Inthis embodiment, the insertion end 24 is formed as a drilling bit. Areceiving hole 28 is disposed in an upper surface of the head end 26 fora screwdriver (not shown) to insert into. The shank 22 has a straightsection with roughly the same outer diameter between the insertion end24 and the head end 26. The straight section includes a lower section 30disposed near the insertion end 24 and an upper section 32 disposed nearthe head end 26. The lower section 30 has rough regular triangulartransverse cross sections. The upper section 32 has circular transversecross sections.

The screw 20 further includes at least one end cutting groove 34. Inthis embodiment, the screw 20 is provided with two end cutting grooves34. The end cutting grooves 34 are disposed in the lower section 30 ofthe shank 22 and extend to a certain length from the insertion end 24toward the head end 26 (as shown in FIGS. 4 and 5). Each end cuttinggroove 34 extends from the insertion end 24 upwardly and slantingly tothe upper right, and an included angle (A) is formed between theextending direction of each of the end cutting grooves 34 and thelongitudinal axis (X). The included angle (A) is between 3 and 9 degrees(see FIG. 4). One or two of the end cutting grooves 34 can be disposedbased on different metals of the shank 22. In this embodiment, the screw20 is made of coated iron and includes the two end cutting grooves 34opposite to each other in a circumference direction of the shank 22 asshown in FIG. 5. The coating on the iron screw 20 is antirust, and thecoating color can be similar to or the same as that of a work-piece foran aesthetic look. However, the screw 20 made of stainless steel canonly include one end cutting groove 34 as shown in FIG. 9. The head end26 of the screw 20 made of stainless steel can also be coated withcoating having the same color as or a similar color to that of thework-piece for an aesthetic look.

The screw 20 further includes a first thread 36 and a second thread 38.The first thread 36 is spirally formed on an outer circumference of thelower section 30 of the shank 22 and includes a plurality ofasymmetrical thread convolutions 40. Each of the thread convolutions 40has a first cutting surface 42 and a second cutting surface 44 (see FIG.8). An included angle (B1) between the first cutting surface 42 and ahorizontal axis perpendicular to longitudinal axis is between 15 and 25degrees, and an included angle (B2) between the second cutting surface44 and the horizontal axis is between 5 and 15 degrees. The secondthread 38 is spirally formed on an outer circumference of the uppersection 32 of the shank 22 and includes a plurality of threadconvolutions 46. An upward spiral direction of the second thread 38 isopposite to that of the first thread 36. As shown in FIG. 2, the secondthread 38 is wound and extended clockwise toward the upper left, whilethe first thread 36 is wound and extended anticlockwise toward the upperright. The upward spiral direction of the first thread 36 is similar tothe upward extending direction of the end cutting groove 34 (upwardlyand slantingly to the upper right). As shown in FIG. 3, a threaddistance (S2) of the thread convolutions 46 of the second thread 38 islarger than a thread distance (S1) of the thread convolutions 40 of thefirst thread 36, which is favorable for speedy screwing of the screw 20.

Referring to FIG. 10, when in use, the screw 20 is screwed intowork-pieces 48 and 50 (such as wooden articles) to be interlockedtogether with the insertion end 24. Since the upward extending directionof the end cutting grooves 34 is the same as the upward spiral directionof the first thread 36 of the lower section 30, and when the insertionend 24 of the screw 20 is screwed into the work-piece 48, the endcutting grooves 34 and the first thread 36 will cut the work-piece 48 atthe same time while screwing into the work-piece 48. Since the firstthread 36 with the triangular cross sections is not in full contact withthe work-pieces 48 and 50, the friction resistance of screwing can bereduced. Furthermore, waste chips produced from cutting the work-pieces48 and 50 will be forced inside the end cutting grooves 34 and thenexpelled outside along the outer circumference of the lower section 30with the triangular cross sections. Therefore, the resistance againstthe screw 20 along the screwing direction can be reduced, and thescrewing speed can further be enhanced. Additionally, when the uppersection 32 of the screw 20 is screwed into the work-piece 48, thescrewing of the second thread 38 can provide a hole expanding effect.Thus, the lower section 30 of the screw 20 will be able to screw intothe work-piece 50 smoothly, and the upper section 32 of the screw 20 canbe embedded into the work-piece 48 completely and tightly. As a result,the work-pieces 48 and 50 can be firmly connected. Furthermore, theasymmetric thread convolutions 40 of the first thread 36 can enhance thecoupling ability of the screw 20, because it is easy to screw the threadconvolutions 40 of the first thread 36 into the work-pieces 48 and 50and not easy to unscrew them.

FIG. 11 shows a screw 20 according to a third embodiment of the presentinvention modified from the first embodiment. In this embodiment, thescrew 20 further includes a non-threaded section 52 disposed between thelower section 30 and the upper section 32 of the shank 22. An outerdiameter (D1) of the non-threaded section 52 is larger than an outerdiameter (D2) of the upper section 32. FIG. 12 shows that after thescrew 20 of this embodiment is coupled with the two work-pieces 48 and50, the non-threaded section 52 is disposed in a junction portionbetween the two work-pieces 48 and 50, which can therefore enhance thestrength of the screw 20 being screwed inside the work-pieces 48 and 50.

FIG. 13 shows a screw 20 according to a fourth embodiment of the presentinvention modified from the third embodiment. In this embodiment, thescrew 20 further includes a plurality of circularly protruding teeth 54formed and spaced apart around an outer surface of the non-threadedsection 52. The protruding teeth 54 help to facilitate fitting thescrews 20 into a screw band (not shown in the drawings) and prevent thescrews 20 from falling from the screw band. Particularly, the screw 20of this embodiment can be prevented from falling off the screw band dueto the vibration of an electric screwdriver during operation.Furthermore, an outer diameter (D3) of the non-threaded section 52 withthe protruding teeth 54 is larger than the outer diameter (D2) of theupper section 32.

When the screw 20 of the present invention is used for screwing into thecompound sheets mixed and compressed from plastic resin and wood chips,the screw 20 can produce outstanding effects. Specifically, the plasticparts of the compound sheets are elastic, and the waste chips producedfrom cutting the compound sheets are mixtures from wood chips andplastic instead of simply powdery wood chips, which cause theconventional screw 10 in FIG. 1 unable to cut and screw into thework-pieces smoothly and unable to expel the waste chips of the compoundsheets smoothly. The designs of the end cutting groove 34 and the lowersection 30 with the triangular cross section can effectively andspeedily cut through the compound sheets and screw into the work-pieces.The waste chips of the compound sheets can be expelled outside along theend cutting grooves 34 and the lower section 30 with the triangularcross section to reduce the resistance against the screw 20 along thescrewing direction. Furthermore, when the screw 20 is screwed into thecompound sheets, the portions of the compound sheets in contact with thescrew 20 will be squeezed upward. The portions being squeezed upward canbe pressed downward by the designs of the opposite spiral directions ofthe second thread 38 of the upper section 32 and the first thread 36 ofthe lower section 30 of the shank 22, and the tight coupling effect canbe achieved.

Thus since the invention disclosed herein may be embodied in otherspecific forms without departing from the spirit or generalcharacteristics thereof, some of which forms have been indicated, theembodiments described herein are to be considered in all respectsillustrative and not restrictive. The scope of the invention is to beindicated by the appended claims, rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are intended to be embraced therein.

The invention claimed is:
 1. A screw comprising: a shank including aninsertion end and a head end spaced from the insertion end along alongitudinal axis, with the shank including a lower section disposednear the insertion end and an upper section disposed near the head end,with the lower section having rough triangular transverse crosssections, with the upper section having circular transverse crosssections, with a first thread spirally disposed on an outercircumference of the lower section of the shank and including aplurality of asymmetrical thread convolutions, with a second threadspirally disposed on an outer circumference of the upper section of theshank, with a non-threaded section disposed between the lower sectionand the upper section of the shank, with an outer diameter of thenon-threaded section being larger than an outer diameter of the uppersection; and at least one end cutting groove disposed in the lowersection of the shank and extending upward from the insertion end towardthe head end, with an included angle formed between an extendingdirection of the at least one end cutting groove and the longitudinalaxis, with the included angle being between 3 and 9 degrees.
 2. Thescrew according to claim 1, further including two end cutting groovesopposite to each other along a circumference direction of the shank,with the upward extending direction of each of the two end cuttinggrooves being the same as the upward spiral direction of the firstthread, with an upward spiral direction of the second thread beingopposite to an upward spiral direction of the first thread.
 3. The screwaccording to claim 1, with the second thread including a plurality ofthread convolutions, with a thread distance of the plurality of threadconvolutions of the second thread being larger than a thread distance ofthe plurality of asymmetrical thread convolutions of the first thread,with the lower section having rough regular triangular transverse crosssections.
 4. The screw according to claim 1, with each of the pluralityof asymmetrical thread convolutions having a first cutting surface and asecond cutting surface, with an included angle between the first cuttingsurface and a horizontal axis perpendicular to longitudinal axis beingbetween 15 and 25 degrees, with an included angle between the secondcutting surface and the horizontal axis being between 5 and 15 degrees.5. The screw according to claim 1, with a plurality of circularlyprotruding teeth formed and spaced apart around an outer surface of thenon-threaded section, with an outer diameter of the non-threaded sectionhaving the plurality of circularly protruding teeth being larger thanthe outer diameter of the upper section.